DEAR CAR TALK: What happens if you put 5 gallons of diesel fuel in a gasoline engine’s fuel tank, but you don’t try to start the vehicle? – Anthony

RAY: Let me guess, Anthony. Asking for a friend?

If you haven’t tried to start the car, you haven’t done any serious damage yet. Once you start the car, the fuel pump sends that diesel fuel into the fuel lines and through the injectors. And that makes a pretty good mess.

But if all the diesel fuel is still in the tank, this is not going to require a home equity loan to fix.

The first step is to have the car towed to your mechanic. Obviously, you don’t want to drive it to him. He’ll drain your gas tank.

Some cars actually have removable drains on their gas tanks. If yours is one of those, you’re in fat city. He’ll just open the drain over an approved container and let the entire contents of the fuel tank come out.

Then close it up, add some fresh gasoline, and drain that mixture to get out most of the remaining diesel. He might even rinse it with fresh gas more than once.

If there’s no drain on your gas tank, your mechanic will have to remove the gas tank and empty it for you. We call that “dropping the tank,” even though we don’t actually drop it. Well, once in a while we drop it.

Anyway, once he dumps out the existing fuel, your mechanic will do the same thing with some fresh gasoline, swishing it around in there to help remove whatever diesel remains. That should get rid of 99.98 percent of that diesel fuel.

Once you’ve drained and cleaned the fuel tank, there’s nothing else you really need to do. Since you never started the car, don’t get talked into replacing any fuel lines, filters, converters, seals or injectors. It won’t be necessary.

Even if you have a little bit of diesel residue in the tank – the stuff that’s still clinging to the walls – when mixed with enough gasoline, it should just get burned up in the cylinders and go out the tailpipe. By residue, I mean ounces, not pints or gallons.

I’d warn you to be careful to not do this again, but I’m sure that after you have to spend a couple of hundred bucks removing the tank, you won’t need any further reminders. Good luck, Anthony.

Got a question about cars? Email Car Talk’s Ray Magliozzi by visiting the Car Talk website, www.cartalk.com.